Iranian Foreign Minister Mohammad Javad Zarif has said that clinching a final nuclear deal with world powers is still "possible."

Zarif said on Twitter on May 18: "Agreement is possible. But illusions need to go. Opportunity shouldn't be missed again."

The comments came after Tehran and six world powers -- Britain, China, France, Russia, the United States, and Germany -- ended a fourth round of nuclear talks in Vienna on May 16 with no reported progress.

Negotiations are due to resume in Vienna next month.

The six powers, known as the P5+1, want Iran to limit nuclear work in exchange for lifting economic sanctions.

Tehran has frozen some nuclear activities for six months in return for minor sanctions relief under a temporary deal that expires on July 20.